Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754199Ab0ALWUY (ORCPT ); Tue, 12 Jan 2010 17:20:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752416Ab0ALWUX (ORCPT ); Tue, 12 Jan 2010 17:20:23 -0500 Received: from mail-px0-f174.google.com ([209.85.216.174]:52105 "EHLO mail-px0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751978Ab0ALWUX convert rfc822-to-8bit (ORCPT ); Tue, 12 Jan 2010 17:20:23 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=WyyZpQo38rflwy2++PsDE+pX3JyX3SPipFCCscSt7F7GG258QWBqpw4PfTVLY1E5YK HyZ54XUMIUJmjLK8v7cb0aGM1U4/fRtoTKLqaOgz3essTTRyIiBMZMVWOaFoZSs7UhRm MQ9+RerhVtfU+jp5QcQJ/UI53ABH8FLeiAjSw= MIME-Version: 1.0 In-Reply-To: References: <1263298146-25597-1-git-send-email-yinghai@kernel.org> <86802c441001121157y5cdc1a91g2a66d8591d6fd579@mail.gmail.com> Date: Tue, 12 Jan 2010 14:20:22 -0800 X-Google-Sender-Auth: 59123ea5e7ed5caf Message-ID: <86802c441001121420y6f585293g341a28030746a512@mail.gmail.com> Subject: Re: [RFC PATCH 1/5] use nr_cpus= to set nr_cpu_ids early From: Yinghai Lu To: Christoph Lameter Cc: Suresh Siddha , Linus Torvalds , "ananth@in.ibm.com" , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1516 Lines: 43 On Tue, Jan 12, 2010 at 12:31 PM, Christoph Lameter wrote: > On Tue, 12 Jan 2010, Yinghai Lu wrote: > >> > Why do we need this twice? >> >> maxcpus only change setup_max_cpus., and if you are using maxcpus=1, >> and you have 8 cpus installed, you can put other >> cpus back online via /sys/interface. > > Hmmm.. Strange semantics since maxcpus=0 disables smp completely. No cpu > can be activated later. Similar to nr_cpus ? no for SMP kernel, when nr_cpus=1 is specified, it looks like only one cpu is installed physically. smp is still enabled. maxcpus=0 is really caused misunderstanding. other maxcpus=1 and other should be rename to boot_online_cpus= > >> nr_cpus= is hard limit nr_cpu_ids, so if you have 16 cpus installed, >> nr_cpus=8 will make your nr_cpu_ids=8, and you can not put back >> other 8 back. and apic mode could stay with logical flat. >> this is used to simulate some debug case. for example you have kernel >> support physflat, and flat, with CONFIG_NR_CPUS=255. to run that on >> system that only have 8 cpus, you will have apic mode in logical flat. >> ?but if you have run the kernel on system with 32 cpus installed, it >> will switch to physflat even you have maxcpus=8 appedded. > > Ok makes sense. good. YH -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/